The present invention relates to a chemical vapor deposition method and apparatus and, more particularly, to a metal organic chemical vapor deposition method and apparatus using an organic metal as a source to form on a substrate a thin film made of a metal constituting the source.
There is a conventionally known chemical vapor deposition method such as MOCVD (Metal Organic Chemical Vapor Deposition) for forming a thin film of a metal or metal oxide on a substrate using chemical reaction of the vapor phase.
FIG. 8 shows an example of a conventional MOCVD apparatus (Metal Organic Chemical Vapor Deposition apparatus). The MOCVD apparatus shown in FIG. 8 forms a PZT film on a substrate 10 in an evacuated reactor 9. Source vessels 1a, 1b, and 1c are respectively heated by temperature controllers 801a, 801b, and 801c to predetermined temperatures, thereby gasifying a lead dipivaloyl methanato complex Pb(DPM)2, an organometallic compound source Ti(O-i-Pr)4, and an organometallic compound source Zr(O-t-Bu)4.
The Pb(DPM)2, Ti(O-i-Pr)4, and Zr(O-t-Bu)4 gases are introduced into the reactor 9 together with an oxide gas such as NO2 or O2 gas to form a PZT film on the substrate 10 using chemical reaction of the vapor phase.
At this time, the flow rates of Pb(DPM)2, Ti(O-i-Pr)4, Zr(O-t-Bu)4, and NO2 gases are respectively controlled by mass-flow controllers (MFCs) 7a, 7b, 7c65, and 7d arranged midway along gas supply paths extending to the reactor 9.
In the MOCVD apparatus shown in FIG. 8, the respective source gases must be introduced to corresponding MFCs at predetermined vapor pressures in order to cause chemical reaction of the vapor phase in the reactor 9. To obtain necessary source vapor pressures, the source vessels 1a, 1b, and 1c are kept at predetermined temperatures.
However, the temperatures are set when respective sources are fully filled in the source vessels 1a, 1b, and 1c. As the sources in the source vessels 1a, 1b, and 1c are gasified and supplied to the reactor 9, the amounts of sources gradually decrease. As the amounts of sources in the source vessels 1a, 1b, and 1c decrease, the source vessels fail to maintain the necessary source vapor pressures.
The same problem arises even when a carrier gas such as He, Ar, or N2 gas is introduced into the source vessel to carry source gases to the reactor 9 by this carrier gas in order to assure predetermined source flow rates. That is, as the amounts of sources in the source vessels decrease upon use, necessary source vapor pressures cannot be maintained, and control of the source flow rates becomes unstable.
To compensate for variations in supply vapor pressure caused by residue variations in the source vessel, for example, an MOCVD apparatus disclosed in Japanese Patent Laid-Open No. 4-362176 is proposed. The MOCVD apparatus described in this reference will be explained with reference to a basic arrangement shown in FIG. 9. In this MOCVD apparatus shown in FIG. 9, pentaethoxy tantalum (Ta(OC2H5)5) serving as an organometallic source bubbled with oxygen and nitrogen for forming an oxygen atmosphere is introduced into a reactor 51 evacuated by a vacuum pump 54. In this case, the flow rate of oxygen introduced into the reactor 51 and that of nitrogen introduced into a material vessel 55 are controlled by signals sent from a flow controller 61 to mass-flow controllers 58.
Pentaethoxy tantalum used in the MOCVD apparatus of FIG. 9, which is a liquid at room temperature, is introduced as a vapor into the reactor 51 by heating the whole material vessel 55 to a temperature of, e.g., 100xc2x0 C. by thermostatic heaters 57, and bubbling pentaethoxy tantalum with nitrogen introduced into the material vessel 55. To prevent pentaethoxy tantalum and nitrogen from liquefying through a gas supply path or pipe extending from the material vessel 55 to the reactor 51, the gas supply path or pipe is heated by gas pipe heaters 56. The gas pipe heaters 56 and the thermostatic heaters 57 are respectively controlled by temperature controllers 59 and 60 which receive outputs from a quadrupole spectrometer 62 (to be described below).
Oxygen and pentaethoxy tantalum introduced into the reactor 51 thermally react by heat energy supplied from an electric furnace 53 surrounding the reactor 51. As a result, a tantalum oxide film Ta2O5 is formed on a substrate 52 placed inside the reactor 51.
The quadrupole spectrometer 62 connected to the reactor 51 detects the concentrations of oxygen and pentaethoxy tantalum introduced into the reactor 51, and outputs an electrical signal when the mass number of pentaethoxy tantalum is around xe2x80x9c405xe2x80x9d. If the concentration of pentaethoxy tantalum represented by the magnitude of the electrical signal is higher than a predetermined value, the temperature controller 59 of the gas pipe heaters 56 and the temperature controller 60 of the thermostatic heaters 57 decrease the temperature of the gas pipe heaters 56 and that of the thermostatic heaters 57. At the same time, the flow controller 61 causes the mass-flow controller 58 to decrease the flow rate of bubbling nitrogen, thereby decreasing the supply amount of pentaethoxy tantalum to the reactor 51. The operation of decreasing the supply amount of pentaethoxy tantalum to the reactor 51 is kept performed until the concentration of pentaethoxy tantalum represented by an electrical signal from the quadrupole spectrometer 62 reaches a desired concentration.
To the contrary, if the concentration of pentaethoxy tantalum represented by an electrical signal from the quadrupole spectrometer 62 is lower than a desired concentration, the supply amount of pentaethoxy tantalum to the reactor 51 is increased under reverse control.
However, various limitations are imposed on the MOCVD apparatus shown in FIG. 9 owing to the use of the quadrupole spectrometer 62 as a measuring device. The usable vacuum degree of the quadrupole spectrometer is structurally limited to a high vacuum range of about 10xe2x88x925 torr or more. The vacuum degree, although it depends on the process, in the reactor during chemical vapor deposition need not be so high, and is as high as about 10xe2x88x921 torr at most. To use the quadrupole spectrometer in this pressure range, a high-vacuum pump such as a turbo molecular pump must be adopted in addition to a reactor exhaust pump to differentially evacuate the reactor.
Hence, when the source concentration in the reactor during the chemical vapor deposition process is to be measured using the quadrupole spectrometer, like the apparatus shown in FIG. 9, the exhaust structure around the reactor becomes inevitably complicated. Even if the quadrupole spectrometer is installed using this structure, a gas component in the reactor is not necessarily the same as a gas component which reaches the quadrupole spectrometer. In addition, some of sources introduced into the reactor are decomposed by a high-temperature wafer heating device, which must be considered. For this reason, it is not practical to compensate for residue variations in the reactor by measuring the source concentration in the reactor during chemical vapor deposition using the quadrupole spectrometer.
It is an object of the present invention to provide a metal organic chemical vapor deposition method and apparatus capable of forming a desired organometallic film by supplying a necessary organometallic source gas more stably than the conventional apparatus.
To achieve the above object, according to one aspect of the present invention, there is provided a metal organic chemical vapor deposition method, comprising the steps of detecting a parameter convertible into the number of moles of gas of an organometallic source supplied from at least one source vessel, heating a source contained in the source vessel when the parameter becomes smaller than a minimum value necessary for forming a thin film of a metal constituting the organometallic source on a substrate in a reactor, and quantitatively supplying the gas of the organometallic source to the reactor, thereby forming the thin film on the substrate.
According to another aspect of the present invention, there is provided a metal organic chemical vapor deposition apparatus, comprising at least one source vessel for supplying gas of an organometallic source, detection means for detecting a parameter convertible into the number of moles of the gas of the organometallic source supplied from the source vessel, and source temperature adjustment means for heating the organometallic source contained in the source vessel when the parameter detected by the detection means becomes smaller than a minimum value necessary for forming a thin film of a metal constituting the organometallic source on a substrate in a reactor, wherein the gas of the organometallic source is quantitatively supplied to the reactor, thereby forming the thin film on the substrate.